The invention relates to a cooling circuit of a liquid-cooled internal combustion engine having a coolant pump, an electrical mixing valve, a radiator, a heater and transmission oil heat exchangers.
Page 156 of the text book Braess/Seiffert: Vieweg Handbuch Kraftfahrzeugtechnik; 1st Edition; October 2000, shows a cooling circuit which is customary for motor vehicles, and which includes a main cooling circuit of an internal combustion engine including a mixing valve (thermostat), a radiator and a coolant pump. The coolant is pumped into the internal combustion engine by the coolant pump, takes up heat in the internal combustion engine, and, at the thermostat, is returned to the internal combustion engine if the coolant is still cool. If the coolant is hot, it is conducted through the radiator in order to dissipate heat. Then, the coolant flows back to the internal combustion engine. The position of the thermostat in the circuit is upstream or downstream of the radiator. In addition, there are also one or more sub-circuits with a heater for heating the interior of the vehicle, an oil-water heat exchanger for heating the engine oil of the internal combustion engine during cold operating states or cooling the engine oil during hot operating states. In addition, the sub-circuit may also include a heat exchanger for the transmission oil, a cooler for the exhaust-gas re-circulation and, under certain circumstances, also a charge air cooler. Moreover, it is known to electrically actuate the mixing valve (thermostat).
It is the object of the present invention to provide a cooling circuit of an internal combustion engine with a transmission of a motor vehicle by which the fuel consumption and the exhaust emissions of the motor vehicle are reduced during operation, in particular during the engine warm-up phase.
In a cooling circuit of a liquid-cooled internal combustion engine of a motor vehicle having a coolant pump, an electrical mixing valve, a radiator, a heater, an engine-oil heat exchanger, a transmission-oil cooler for transferring heat to the ambient air, a transmission-oil/cooling water heat exchanger between the transmission oil and the cooling water arranged in parallel flow circuit with the transmission-oil cooler, and an actuator for controlling the oil flow, an electrical mixing valve is arranged in the cooling water line to the radiator/transmission-oil cooler and the transmission-oil/cooling water heat exchanger, such that the heat transfer in the transmission-oil/cooling water heat exchanger can be controlled by controlling the coolant flow through the transmission oil/cooling water heat exchanger and the radiator.
By means of the actuator, the oil flow of the transmission is distributed as a function of the quantity and direction of the heat flux in the oil. If the transmission oil is cold, the whole oil flow is conducted through the transmission-oil/cooling water heat exchanger, so that the transmission oil is heated by the engine-cooling water. Rapid heating of the transmission oil reduces the friction in the transmission and therefore the overall fuel consumption of the motor vehicle. When the transmission oil is hot, the transmission oil is passed to the transmission-oil cooler, by switching over the actuator, in order to dissipate the heat to the environment and to prevent overheating of the oil. If the transmission oil is hotter than the engine oil, as it may occur, for example, during prolonged periods of driving downhill, the actuator is used to direct the transmission oil flow to the transmission-oil heat exchanger, in order to control the temperature of the engine oil.
Moreover, the heat transfer in the transmission-oil heat exchanger can be controlled by the fact that the cooling-water stream through the transmission-oil heat exchanger can be controlled by means of the electric mixing valve. Controlling the cooling-water flow through the transmission-oil heat exchanger allows better matching of the heat transfer from the transmission oil to the cooling water or vice versa, since, by setting different quantitative flows of cooling water with an approximately constant quantitative flow of transmission oil, it is possible to set the required heat transfer to the cooling water without dissipating heat to the environment via the transmission-oil cooler.
In a particular embodiment of the invention, the actuator is controlled as a function of various operating parameters, such as ambient temperature, cooling-water temperature, driving speed or engine speed. This makes it possible to control the heat transfer as required.
In a further embodiment of the invention, the actuator is controlled as a function of the temperature of the transmission oil. The actuator may simply be controlled as a function of temperature, for example, by means of a temperature-dependent expansion regulator (thermostat). This is a simple and inexpensive option for implementing the actuator for transmission-oil distribution.
In a further advantageous embodiment of the invention, the actuator can be controlled by a control unit. If a plurality of parameters are to be included in the control characteristic, it is advantageous for them to be controlled jointly by a common control unit. This allows regulation on the basis of a parameter-dependent characteristic diagram, in order to allow heat transfer, which is optimized with regard to consumption and emissions of the motor vehicle.
In a favorable embodiment of the invention, the actuator is arranged downstream of the transmission-oil cooler and the transmission-oil heat exchanger. In this case, the actuator is arranged at the point at which the two partial streams from the transmission-oil cooler and the transmission-oil heat exchanger join to form a common oil return line. Arranging the actuator downstream of the heat-releasing or heat-absorbing components allows good regulation, known as output regulation, of the transmission-oil temperature, since the actual temperature of the oil flowing back can be accurately controlled.
As an alternative hereto, an embodiment of the invention with the actuator upstream of the branch to the transmission-oil cooler and transmission-oil heat exchanger is possible. This embodiment is known as input regulation and, although having a slightly lower regulation quality than output regulation, offers a variant, which may be required under certain circumstances for reasons of lack of installation space.
In a further favorable embodiment of the invention, the cooling-water side of the transmission-oil heat exchanger is connected in parallel with the radiator. In this embodiment the transmission-oil heat exchanger is arranged in what is known as the short-circuit line between the electrical mixing valve and the coolant pump. This short-circuit line is already present in the cooling-water circuit, and therefore no additional structural outlay is required. The electrical mixing valve allows the cooling-water flow in the transmission-oil heat exchanger to be controlled in addition to the oil flow. With this arrangement, it is possible, for example in the warm-up phase, to direct all the cooling-water through the transmission-oil heat exchanger, in order to provide for rapid heating of the transmission oil.
In a further alternative embodiment of the invention, the cooling-water side of the transmission-oil heat exchanger is connected in series with the heater in a subcircuit. An engine-oil heat exchanger may be connected in parallel or in series with the transmission-oil heat exchanger. With this arrangement, the transmission oil can be at least partially heated even when the short-circuit cycle is completely closed during the starting phase of the internal combustion engine. Even in the cold-start phase, somexe2x80x94although under certain circumstances only a very small amountxe2x80x94of the cooling water flows through the heating circuit. This allows heat transfer from the heated cooling water to the engine oil and the transmission oil, so that the friction in the internal combustion engine and in the transmission is reduced by the heated oil.